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2445 LED - Attenuator relays - V/DIV - SEC/DIV problems

 

Hello to everyone. I am new here and I don't speek English very well, so sorry for any mistakes.


Before some weeks, I have bought an Tektronix 2445 oscilloscope from ebay.


It have at least two problems:


The first is that the front panel leds and the attenuators relays don't working. I have replace the U3300 (74LS164) with a new one and now in Channel 2 lights the 1M¦¸ DC led and in Channel 1 lights 1M¦¸ AC and DC leds together, but it don't have any respond when I trying to change the state. In the scale factors of CRT i can see that responds on changes.
The second is that the V/DIV and SEC/DIV knobes is stucked in the .1V/DIV and in 1SEC/DIV. In CRT the Scale Factors is ok in any position but the waveform is like i have set it in .1V/DIV and 1SEC/DIV. When i trying to change any VAR knob the waveform responds properly. I have replace all electrolytic caps in the PSU, but I dont have the correct size for the plastic caps. The DC voltages are ok, but i don't know if the ripple that i see in a second oscilloscope it's ok (maybe becose the second it's a little bit slow DSO).
The XTAL of A5 board was broken and I have replace it with a new 10MHz. I replaced even the electrolytic and plastic capacitors of A5 board but nothing.


Any suggestions on what to check? I will have second oscilloscope for testings the Monday and the Tuesday but after i will have to wait until 5-10 January.


I will upload a video on youtube to see the problems.


Thanks in advance,
Stamatis Aronis
 

The LEDs and the Attenuator relays are back.

I don't know why, but i have the idea to disconect the J652 from the A5 board, and when I power up the oscilloscope the relays worked. So I thought to try to remove the shift registers from A6 board to see if is some broken. First I remove the U3375 which was easier. I connect back the A6 board and the relays working properly but the leds dont. After of that I have tried to add a new 74LS164. The LEDs after that worked properly and the same with the relays.


I do not know whether it matters, but the U3300 and the U3375 that I have replaced has the same datecode (V8333) from SB (?) manufacturer.




BUT, the other problem (with knobs) it's here, so any suggestions will help.


Thanks in advance,
Stamatis Aronis



P.S. I dont have upload the video yet.
 

Hey Stamatis,

welcome to the group. Congrats on your beautiful new/old scope, and on your repairs so far. Sounds like your 2445 has been through some hard times, I'm glad to see she's found a caring owner :).
Please post that video, I've a feeling it'll help, if only by jogging the memories of the Tek repair veterans here.


Siggi
 

The video is here: Tektronix 2445 Problems



Tektronix 2445 Problems This feature is not available right now. Please try again later.



View on www.youtube.com
Preview by Yahoo



Sorry for the bad quality of the video; ¦© haven't see that the camera was on 240p mode.


Eventually the V/DIV knobs work properly. But the SEC/DIV don't working. Or, at least don't working properly.
 

Hey Stamatis,


This is working as intended. The 2445/2465 scopes have an interesting calibrator that tries to keep a fixed number of cycles on screen - to a point. You'll notice that at the highest couple of speeds it gives up.


You can check this on the B sweep. Set the A sweep to 1ms/div or so, pull out the button and go to the next higher speed. You're now in intens with both A and B sweeps showing. Push the button back in to go to B sweep only, and you'll see your calibrator stays at the A sweep speed.


Siggi
 

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Ok, I have connect an external signal and its working properly.

Thank you all for your time!


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